Figure 2.

Ribbon representation of the ACT α-subunit dimer. One monomer is color coded according to the secondary structure, with β-strands in green, α-helices in red and loop regions in yellow. The second monomer is gradient color coded from blue at the N-terminus to red at the C-terminus. Three Mg2+ ions are shown as cyan spheres. Two of the Mg2+ ions are bound to identical sites in molecules A and B and one is bound at the monomer interface near the non-crystallographic symmetry twofold axes. The figure was produced with the program ICM (Abagyan & Totrov, 2000).